1. Field
This invention relates generally to semiconductor device manufacturing, and more specifically to treatment of lead ends of flat-pack no-lead semiconductor device packages.
2. Related Art
A lead frame strip (hereinafter “strip”) is populated with a plurality of lead frames. A semiconductor or microelectronic device is mounted on each lead frame and encapsulated with a mold compound. Lead frames are separated during singulation of the strip to create individual semiconductor or microelectronic packages (hereinafter “package(s)”). A package utilizes leads for externally providing and receiving signals and power. One type of package is a flat-pack no-lead package where each lead, or terminal, is exposed at a bottom and at a side of the package.
Most known methods of manufacturing flat-pack no-lead packages result in leads that have at least some exposed base metal on an end, or flank, of each lead. An oxide coating forms on surfaces of base metal of the lead frame that become exposed to air as result of being cut during singulation. Typically, the base metal of the lead frame of a flat-pack no-lead package is copper (Cu), and the oxide is a copper oxide, for example, Cu2O, CuO and CuO2. Solder tends to adhere to a surface that is solder wettable; however, copper oxide is not solder wettable.
Solder paste includes solder and flux. A purpose of flux is to clean and activate a surface of a base metal. There are different activity levels, or strengths, of flux. Higher activity levels can prepare surfaces that have more oxide and/or contaminants. Flux removes any oxide that may have formed on the surface of a cut end of a lead, thereby allowing solder to more readily adhere to the cut end of the lead.